A highly sensitive gravimeter system is important for measuring small variations of local gravitational field for various applications in petroleum, geophysics, or civil engineering. For instance, examples include the detection of mining or hydrocarbon reserves, the detection of magma build-up before volcanic eruptions, and subterranean tunnels. See, for example, R. P. Middlemiss et al., “Measurement of the Earth tides with a MEMS gravimeter,” Nature, vol. 531, pgs. 614-617 (March 2016) (16 total pages) (hereinafter “Middlemiss”).
Several technologies exist for detecting variations in a local gravitational field, such as pendulum-based systems, free-fall systems, spring-based systems, superconducting gravimeters and atom interferometers. However, while precise, these systems are very expensive (>$100,000), bulky (>8 kg), and not portable.
These drawbacks have motivated the search for lower cost high sensitivity gravimeter systems, such as the microelectromechanical system (MEMS) system described in Middlemiss. While very sensitive, a MEMS gravimeter has several notable drawbacks. The MEMs device uses a silicon cantilever, with limited oscillator quality factor (Q) and the cantilever spring constant which could be temperature sensitive or change over time. Thus, inaccurate readings may be obtained unless regular recalibrations are performed.
Accordingly, an improved low-cost, high-sensitivity gravimeter would be desirable.